As is disclosed in, for example, JP, Y2 No. 58-32578, a drive assembly for propelling a walking mower according to the prior art is, in general, fashioned such that it transmits power of an engine to left and right drive wheels without a speed-change control and only with a speed-reduction control. Further, this kind of drive assembly is fashioned to include a clutch, operable to interrupt transmission of power to the drive wheels, for enabling an operator to move the mower by pushing or pulling same and for an easy turning operation of the mower by the operator. This clutch is, in general, fashioned such that it is kept in its disengaged condition by a clutch spring and is brought into an engaged condition when a clutch lever affixed to a steering handle is grasped.
Meanwhile, it is believed very convenient if speed of a walking mower could be selected from plural variable speeds in accordance with height and/or density of turfs, operator's liking and so on. Further, it is wished to travel a walking mower with a relatively high speed when the mower is not used for mowing and is merely travelled.
There is known from JP,A(U) No. 62-193815 a drive assembly for walking mowers which includes a speed-change mechanism, although it provides only two variable speeds. In this known drive assembly, a ball clutch is disposed within a transmission casing at a driving side of the speed-change mechanism. When a shifting operation of the speed-change mechanism is carried out, the clutch is once disengaged for lightening the operation.
However, there is a limit, in the structure known from JP,A(U) No. 62-193815, with respect to the lightness of a shifting operation. This is because, even when the clutch at the driving side of a speed-change mechanism has been disengaged prior to a shifting operation of the change mechanism, the speed-change mechanism remains connected with left and right drive wheels so that speed-change gears cannot be freely rotatable due to a resistance applied from the side of drive wheels and, therefore, a resistance against the shifting operation is provided.
Further, even when the clutch has been disengaged for an easy moving or turning of the mower by an operator, the mower is moved or turned by the operator under a condition where a rotational motion is provided to one of speed-change gear trains of the speed-change mechanism by the drive wheels which are rotated as the mower is moved or turned. Consequently , a speed-change gear train which also functions as a speed-reduction gear train may provide a resistance against the operator's mower-moving or -turning operation.
In a self-propelled walking mower, left and right rear wheels are, in general, used as drive wheels. It is often experienced, when such mower is started to travel by engaging a ball clutch or a dog clutch, that a floating state of front wheels is caused due to a too quick engagement of the clutch.